Article found in The Illustrated London News magazine of 17 September 1904.
The essential features of a Pneumatic Tube Line are four: a suitable conduit, or tube; a carrier for passing through the tube; a transmitter, or device for dispatching the carrier; and a receiver, or apparatus for arresting the carrier and delivering it from the line. The problem of a suitable conduit is not nearly so simple as it may seem. At the time when the construction of the first large tube line in Philadelphia was undertaken, no pipe or tube of a suitable nature could be purchased in the market. Experiments were made with pipes of various sorts, until the invention of a special machine for boring cast-iron pipes finally gave the advantage to this material, and it has been adopted in all subsequent constructions. The pipes are bored smooth a gun-barrel on the interior, and the ends are turned and counterbored so as to ensure alignment, and at the same time to permit sufficient angle between consecutive lengths to admit of a considerable deflection when it is desired to avoid obstructions. The carrier adopted for the present system travels upon a pair of bearing-rings near each end of it. These are of specially prepared composition, and will cover ten thousand miles before they are worn out. The transmitters are of several different types. The first requirement is that they shall introduce the carrier into the air-current without interrupting the flow, and that the operation shall be as simple as possible. The latest form of transmitter accomplishes this without other act on the part of the operator than that of dropping the carrier into the opening in the floor.
The receivers are of four types, each adapted for some special situation or condition of operation. The simplest as well as the newest is without moving mechanism of any kind, and this is the type exhibited by Mr. Batcheller at Ranelagh Lodge, Fullham. In each of the other three types the carrier is brought to rest by the air-cushion formed ahead of it in entering the closed section of tube. When placed where the pressure of the line is atmospheric, the carrier is automatically discharged by the opening of the gate that normally closes this section; where the pressure of the line is above that of the atmosphere a special form of receiver is prohibited, which delivers the carrier without escape of air. When it is desired to connect several stations on a single line and to be able to dispatch from one end of the line top any of these stations, an automatic machine, called the "intermediate receiver," is provided. By means of metallic discs of graduated diameter borne on the front end of the carrier, this machine selects the carriers intended for delivery and passes all carriers for stations beyond.
The author of this article is unknown. Since it is published far more than 70 years ago, it is believed to be in the Public Domain.